This invention relates to a silencer for an outboard motor, and more particularly to an improved silencing and air delivery device for a marine propulsion engine.
As is known, marine propulsion engines generally must be extremely compact in nature. This is particularly true with respect to the power head of an outboard motor wherein the engine is contained within a protective cowling. The induction air for the engine is delivered through an opening in the protective cowling, and this opening is generally configured so as to exclude as much water as possible from the air introduced to the interior of the protective cowling. The air is then delivered from the interior of the protective cowling to the charge formers of the engine for engine operation.
It is well known that the induction system air is one of the large sources of potential engine noise. Of course, if a large plenum chamber supplies air to the induction system, then silencing can be achieved. However, it is difficult with the compact nature of outboard motor power heads to employ such large plenum chambers.
The problems attendant with prior art constructions can be best understood by reference to FIGS. 1 and 2, which are respective side and top elevational views of the power head of a conventional outboard motor with the protective cowling being shown in cross section in FIG. 1 and with the main cowling member removed in FIG. 2. The power head is identified generally by the reference numeral 11, and it can be associated with any type of propulsion unit, such as a propeller or the like, which are driven in well-known manners. The power head 11 is comprised of an internal combustion engine 12 and a surrounding protective cowling that is comprised of a lower tray portion 13 and an upper main cowling portion 14.
The upper main cowling portion 14 is, as is typical with conventional outboard motor practice, provided with a rearwardly facing air inlet opening 15 through which atmospheric air may be delivered. This opening feeds a cavity 16 formed by the main cowling member 14 and a cover piece 17 thereof. A vertically extending air inlet duct 18 extends through a lower wall 19 of the main cowling member 14 and permits air to be introduced into the area around the engine 12, as shown by the arrows in this figure. The configuration of the cowling inlet device described is designed to promote water separation.
The engine 12 may be of any type that is well known in this art and in the illustrated embodiment as being depicted as a V-6, two-cycle, crankcase compression engine. As is typical with outboard motor practice, the engine 12 is disposed so that the crankshaft, which rotates in a crankcase chamber 21, is disposed about a vertically extending axis. The crankcase chamber 21 is disposed at the forward end of the protective cowling and has, as is typical with two-cycle engine practice, individual crankcase chambers associated with each of the cylinders of the engine which are sealed from each other.
The engine 12 is provided with an induction and charge forming system, indicated generally by the reference numeral 22, which is comprised of a combined intake manifold reed valve assembly 23 that is affixed to the crankcase member 21 and contains induction passages and reed-type check valves for permitting a charge to flow from the induction system 22 into the individual sealed crankcase chambers for compression. The read-type check valves preclude reverse flow when the charge is being compressed, as is well known in this art.
A plurality of charge formers, in this illustrated prior art type of construction, three vertically spaced two-barrel carburetors 24a, 24b, and 24c supply a fuel-air charge to the runners of the manifold 23, with each throat or barrel of a carburetor serving a respective crankcase chamber.
An air inlet and silencing device, indicated generally by the reference numeral 25, is provided, and this comprises a generally longitudinally extending plenum chamber having outlet openings that communicate with the throats of each of the carburetors 24a, 24b, and 24c. This inlet device 25 has pairs of inlet openings 26a, 26b, and 26c which are aligned with the respective carburetors 24a, 24b, and 24c, and which induct the air from the interior of the protective cowling, as shown by the arrows in FIGS. 1 and 2.
Obviously, this type of arrangement, although it is designed to provide some silencing, cannot be very effectively tuned to silence particular engine speed ranges. In addition, this type of arrangement presents some risk that water may enter the rearwardly facing inlet openings 26a,b,c.
It is, therefore, a principal object of this invention to provide an improved air inlet and silencing device for an outboard motor.
It is a further object of this invention to provide an improved air silencing device for the charge formers of a marine propulsion unit that is contained within a protective cowling, but which can be provided with silencing devices that can be tuned.
It is a further object of this invention to provide an improved air inlet system for the protective cowling of an outboard motor wherein the air is introduced to the interior of the protective cowling in such a way that water is less likely to reach the charge formers and induction system of the engine.